The present invention relates to low pressure gas discharge lamps and, more particularly, to a method of hermetically sealing vacuum ports in low pressure gas discharge lamps or bulbs and the products of the method.
Type of flat plate illumination display lamps exist in the field. Examples of these lamps or bulbs are illustrated in U.S. Pat. Nos. 4,584,501 entitled "Flat Plate Luminous Display Device", issued Apr. 22, 1986; 4,990,826, entitled "Low Voltage Gas Discharge Device", issued Feb. 5, 1991; 5,036,243, entitled "Glass Plate Illumination Device Sign with Integral Electrodes of Particular Thermal Resistance", issued Jul. 30, 1991; and 5,066,257, entitled "Process for Producing Flat Plate Zllumination Devices", issued Nov. 19, 1991, the specifications and drawings of each are herein expressly incorporated by reference. These flat plate lamps are manufactured by different methods and all illustrate varying elements. However, one element which all of the flat plate lamps have in common is an evacuation tube which extends from the flat plate to enable drawing of a vacuum from within the lamp and acts as an entrance port toy rare gases.
During the final processing of the low pressure gas discharge lamps, the lamps are evacuated, filled with the appropriate rare gases, and are hermetically sealed. In practice, this process is done through a relatively small diameter glass chip or tube which is added to the lamp plate by fusing it or soldering it, with a special low melting temperature glass, to the plate. Ordinarily, this solder and tube have an expansion coefficient which is equal to that of the glass plate.
After processing the lamp, the evacuation tube or chip is heated to a softening point whereby the relative vacuum within the lamp channel collapses the wall of the tube and fuses the tube sides together to become solid and thus, vacuum tight. The excess glass is removed, leaving a relatively short piece of evacuation tube extending from the lamp. This piece of the evacuation tube is highly fragile and requires physical protection from damage, which damage in every case will result in lamp failure.
In the case of fluorescent tubes, the remains of the evacuation tube, which is sometimes referred to as tip offs, are protected by the lamp cap which also acts as an electrical connection to the cathodes. When the lamps area not tubular, but formed in a glass plate or other designs, the evacuation tube is added to one of the plates and after processing, the tube extends from the same plate adding extra dimensional length to the lamp as well as requiring a physical protection, such as a cap which is seen in FIG. 1.
Also, in a number of processes, a getter is added to the lamp which is activated after the lamp has been fully processed. The getter's function is that of a chemical sponge to absorb and neutralize contaminants which would effect the proper functioning of the lamps. In order to activate the getter, it must be heated to an elevated temperature for a given period of time during which the absorption of undesirable elements such as hydrogen, oxygen and the like elements which it is designated for, takes place.
As mentioned above, these prior lamps, while working satisfactorily for their intended purpose, have an additional thickness created by the cap protector on the evacuation tube. Thus, it would be desirable to provide a low profile, low pressure gas discharge lamp having a substantially flush cover which enables the lamp to hang substantially parallel with a holding surface.
It is an object of the present invention to provide such a lamp and a method of making the same. The present invention provides the art with a low profile, low pressure gas discharge lamp or bulb having extremely high physical integrity. Also, the present invention has a cover plate which is hermetically sealed with the glass plate providing a vacuum tight seal.
The invention provides a cap which may be coupled with a getter so that the getter may easily be applied and activated within the lamp. Further, the present invention replaces the evacuation tube with a metallic cover. The cover has substantially the same coefficient of expansion as the glass plate of the lamp. The present invention provides a method for carrying out the manufacturing of such a plate glass lamp.
From the following detailed description taken in conjunction with the accompanying drawings and subjoined claims, other objects and advantages of the present invention will become apparent to those skilled in the art.